It could be either too much dampness or a fungal disease if it seems to be spreading. In any case, I think the best solution would to be to cut back on the watering, pull out any nearby weeds and aerate the first couple inches of the soil by hand.

If it looks like my bartzella where it looks like there are spots of the leaves that are dried up, that would likely be related to sun burn which occured while the leaves were still growing.

Here is a link that might be useful: Bartzella with browning from sun burn

Steve, it's exactly what it is on my Bartzella! How can we prevent further browning or would that be all? Thanks so much for the reply!

I believe that if they are not watered when there is full sun out, they should not have any further browning. Mine appears to have stabilized now that the leaves are completely grown.

They seem to be the most sensitive to the sun throughout May when the leaves are still actively growing, and soft, but they should be hardened off already in June.